Weather service issues flooding advisory ahead of king tide

Sylvie Lee walks through a puddle created by king tides after picking up plastic bottles floating in the bay at Pier 14 along the Embarcadero in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide conditions are causing higher than usual water levels. less

Sylvie Lee walks through a puddle created by king tides after picking up plastic bottles floating in the bay at Pier 14 along the Embarcadero in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide ... more

Sylvie Lee walks through a puddle created by king tides after picking up plastic bottles floating in the bay at Pier 14 along the Embarcadero in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide conditions are causing higher than usual water levels. less

Sylvie Lee walks through a puddle created by king tides after picking up plastic bottles floating in the bay at Pier 14 along the Embarcadero in San Francisco, Calif. on Tuesday, Nov. 24, 2015. King tide ... more

The National Weather Service issued a flooding advisory for low-lying areas on the coast and bay on Saturday as Northern California is expected to see among the highest tides of the year.

The so-called "king tide" is the highest tide of the year and occurs in December or January when the sun and moon reach their closest point to Earth, causing the ocean to bulge from the gravitational pull.

Areas expected to be overrun with water include the Embarcadero and bayside parking in San Francisco, the Watsonville Slough, areas along the Monterey Bay and Pajaro Dunes.

In San Francisco, the high tide is predicted to reach 6.87 feet at 10:20 a.m. Saturday and low tide at -1.33 feet at 5:09 p.m. The level of the sea will shift some eight feet in about seven hours.

A similar scenario will occur Sunday with high tide at 11:50 a.m. and low tide at 5:54 p.m., and National Weather Service meteorologist Ryan Walbrun assumes another advisory will be issued.

While the National Oceanic and Atmospheric Administration predicts tides over six feet on Dec. 22 and Dec. 23, Brian Garcia, a meteorologist with NWS, says other environmental factors could raise them even higher, potentially causing minor flooding in low-lying coastal areas.

"Predicting tides is really easy as they've tracked them for so long and the mathematics can tell you exactly how much the water is going to rise," says Garcia. "Where it differs, year to year, are tidal anomalies. Those tidal anomalies are anything that makes the water level higher or lower than predicted."

In coming days, one anomaly that could exacerbate the tides is above-normal water temperatures. In December, Northern California temperature readers for the Pacific Ocean are usually in the mid-50s, but in recent weeks they've been in the high-50s and even brushing with 60 degrees in Monterey Bay. Warmer waters can cause thermal expansion, leading ocean waters to rise a couple inches above tidal tables.

Big swell and incoming storms can also impact tides but are unlikely to play big roles in this weekend's scenario. On Friday afternoon, buoys off San Francisco were reading wave heights of 8 to 11 feet, a moderate height that's unlikely to push water farther up the beaches.

Storm systems are headed for the Bay Area Sunday and Monday, but again probably won't push the tides much higher.

"Right now, it doesn't look like the storms are going to play a significant role in the exacerbation of the king tides," he said. "Winds won't be set up right."